How does Mobile Originated (MO) SMS Work (through an SMS Gateway)?

SMS messages are sent from phone to phone and phone to application through the SMS gateway. If you ever wondered how SMS text messaging works, read here…

We’re all used to receiving SMS messages sent through an SMS gateway (nearly all of them are). Some of us receive dozens every day, sent by friends from their mobile handsets, or to alert us of breaking news, weather updates, or product specials.

But few people are aware of the complex internetworking that needs to occur for an SMS generated on a handset to complete the journey to its intended recipient. Simplified, here are 6 steps that illustrate how an SMS message from Jack gets to Jill through an  SMS gateway.

1. Jack types out the message on his phone, selecting Jill as the recipient. His phone is configured to use a specific SMS Centre (SMSC) for its SMS submission. The handset sends the message to this SMSC.
2. The SMSC processes the received message by doing a lookup against the HLR, or Home Location Register. The HLR will informs the SMSC of the location of the Mobile Switching Centre (MSC) of Jill’s number.
   Jill’s number identifies her mobile telephone operator and it is with this that the MSC is associated.
3. The SMSC then passes the message on to the MSC related to Jill’s number. The MSC must now establish where the handset for this number is and so does a lookup against the VLR (Visitor Location Register) which tracks the presence of a handset on the network.
4. The MSC uses the result of the VLR lookup to send the message via an SMS gateway to the relevant mobile server which then delivers the message to Jill’s handset.
5. After the above steps have been completed, Jill’s MSC informs Jack’s SMSC of the status. If Jill’s number is valid, but phone not reachable, retries will occur for the duration that Jack’s phone has set, or the mobile networks involved permit.
6. If successfully delivered, Jack’s SMSC will then send a delivery receipt, through the SMS gateway, back to his handset if he had opted to enable this requirement when sending.

For MO messages that are directed at a service (typically represented by a short number of 5 digits) rather than an individual, step 4 onwards will differ in that the message would be delivered to a connected server associated with that short number, rather than to a physical handset. SMS-based competitions (made possible through an SMS gateway) will typically be handled in this way – MO messages processed by a program where a winner can be identified by sender number.

Need more information? Follow the link to the SMS gateway page.

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Tags: mobile originated SMS, SMS competitions, sms gateway, sms gateways